Happy My Vacation Week, everybody! Two things this week: First, this whole "Korean War" thing, and specifically the part it played in the Great American Tank Panic of the 1950s, of which I think precisely no-one who is not a tank enthusiast of the first water recalls. Second, Our Alex sends us to Dmitry Yudo's Overlord blog, where Our Host tells us about something exciting he found in the British archives, specifically, "plastic armour." The two things may or may not go together. 
Before I get into anything else, I should mention the Overlord's conclusion, which was that "plastic armour" might disappear from British archives at the end of the war because of a Top Secret rating stamped over it leading into the Burlington/Chobham armours of the 1960s that are such a fascinating and unwritten story of postwar materials science development, with its applications well beyond militariana, to include, for example, semiconductors. The problem with this fascinating thesis that mention of plastic armour stops in 1945, while the first applique composite armours following the Burlington/Chobham scheme do not appear until the 1950s. One would expect some kind of accommodation to applique schemes on, for example, the later marks of Centurion, but the cast armour turret really doesn't seem designed to take an applique plate.
Ahem. Let's put that dangling, tantalising thought from our minds for a moment and follow the other lead, the Korean police action.
If you're wondering about the relevance of my vacation to this, I went to see my Mom, and, in my hurry to pack up and leave on Sunday morning, continued to fail to find a book that I had stocked my library with many years ago and ignored ever since: Bruce Cummings' Korea's Place in the Sun. *As a result, I couldn't read it over the week, although I got well into Kim Stanley Robinson's 2150 AD, and there was also a distracting election in a neighbouring third world nation.
Upon return, in the bright morning sun, Cummings of course practically jumped into my hands, which is just as well considering that the Robinson book has disappeared into the jumble. (Or I lost it on the bus. I hope I lost it on the bus.) I've been feasting on it all morning instead of running various important errands, and it makes a very useful corrective to Halberstam's Coldest Winter, a history of the Korean War that could easily be retitled Kim Il Sung: My Part In His Downfall, by Averill Harriman.
The upshot of contemplating the history of the Korean War from the perspective of a historian of Korea rather than that of a historian of Washington office politics is that the way that the Korean War emerged from an ongoing Korean civil war turns out to be in a way that's a lot less easy to understand.
The received account, according to Halberstam, filtered through a lot of contemporary Time magazine reporting, is that the Inmun gun (that's how we professionals say "Korean People's Army") invaded the South in a concerted blitz that massively outnumbered the southern army.
In fact, it would appear after having to tolerate provocations from the Rhee regime through 1949, the return of the large Korean contingent fighting with the PLA had given Kim Il Sung the capacity to respond to the next provocation with a counterattack. The regime wished to capture the Ongjin peninsula and the holy city of Kaesong, which apart from generalised nationalist aspirations, threatened Pyongyang with a "pincer attack," at least in the professionally paranoid minds of the northern military leadership. Generalised counterattacks along the front were envisioned, since Kim was in no position to deny any of his generals their share of glory, and, in any case, what was the worst that could happen? In particular, the 3rd and 4th Infantry Divisions and 105th Armoured Brigade of the Inmum gun was set to pitch in to the South Korean 1st and 7th Divisions, guarding the direct approach to the capital. 
At this point, Cummings, although no friend of the regime, becomes downright elliptical, completely evading, for example, the notorious prison massacres carried out by the Rhee regime while speaking of the "some" who believe that there "was an element of fifth column" activity in the defending South Korean force. It is more commonly asserted, as Time proposes, that the defenders were outnumbered and lacked any antitank assets. About antitank assets it is hard to speak clearly, considering the random assortment of equipment that the occupying Americans had left in Korea --the southerners wer certainly not short of artillery, for example; but it seems clear that the Inmun gun was outnumbered. On the other hand, it had air supremacy, something of which modern military historians attached to land forces never seem to be quick to comment upon. 
The way in which mid-century land forces without air superiority consistently collapse for mysterious reasons of morale and leadership really is quite striking. But, of course, we're not here to hear about boring old Yak fighters and Ilyushin light bombers that only exist because mad air marshals want to strategically bomb nations into oblivion. (Not that that isn't a thing by Korea, but anyway.) We're here to hear about Panzer panic! American generals reduced to leading tank-hunting parties because their soft and undertrained troops have lost faith in their bazookas!
And, as the hitherto uncommented-upon marginal pictures suggest, the absolute wig-out conducted by the American armoured forces during the 1950s. I'm not going to delve too deeply into the industrial side of this story. The short design histories of the American tanks of the era discuss the manufacturers, factories, Congressional hearings and scandals that flowed from the tank panic. In instantiated terms, we have the M26 Pershing; the M41 Walker light tank; three tank designs named for General Patton, the M46, M47, M48 (Pattons); the M103 heavy tank, which never got named after anyone; and the T69,
which seems to be the only one of three different T-series prototypes to get its picture in the news. That is a lot of new tank designs for a half-decade or so! From these we get a pretty clear view of what armoured forces designers considered important in the mid-Fifties, and alas for Overlord's blog, it is not unconventional armoured schemes.
The way in which mid-century land forces without air superiority consistently collapse for mysterious reasons of morale and leadership really is quite striking. But, of course, we're not here to hear about boring old Yak fighters and Ilyushin light bombers that only exist because mad air marshals want to strategically bomb nations into oblivion. (Not that that isn't a thing by Korea, but anyway.) We're here to hear about Panzer panic! American generals reduced to leading tank-hunting parties because their soft and undertrained troops have lost faith in their bazookas!
And, as the hitherto uncommented-upon marginal pictures suggest, the absolute wig-out conducted by the American armoured forces during the 1950s. I'm not going to delve too deeply into the industrial side of this story. The short design histories of the American tanks of the era discuss the manufacturers, factories, Congressional hearings and scandals that flowed from the tank panic. In instantiated terms, we have the M26 Pershing; the M41 Walker light tank; three tank designs named for General Patton, the M46, M47, M48 (Pattons); the M103 heavy tank, which never got named after anyone; and the T69,
Well, that's not entirely true, at least of the Americans. A composite fused silica armour applique was proposed for the M48. It was mainly favoured for protection against HEAT and HEP, that is, against thermal gas jet penetration modalities rather than kinetic, but at least the turret was to be manufactured of the new material, so there was considerable faith in its ability to withstand 85mm penetration. (The main Red Army kinetic-kill antitank weapons being still thought to be the 76 and 85mm guns, with the monstrous 122mm of the JS-series intended to defeat thick German wartime armours by throwing a giant blob of shell at them.) This was shelved because the contractors, "OTAC and Carnegie Institute of Technology" were hopelessly behind, and not by revelations about the existence of the T54/55's 100mm and succeeding 114mm guns. However, the fused silica armour remained in development until 1958, and might well have been dropped due to word out of Beddington/Chobham. I don't know!
Unfortunately for Overlord, this work started in 1952, still leaving a seven year gap in which there is no particular reason for Plastic Armour to be secret. You can see the traces of a conceptual line, but I suspect that, if it were secret, it doesn't run through tank stuff, but rather the main line of Big Secrets that the military industrial complex was worrying itself over at the time. 
Boom! Like this, only with more radiation.
So the problem that's facing the Plastic Armour guys in the mid-war years is that Plastic Armour gets more effective the faster the projectile that is fired at it; but, also, it seems unreasonably effective against the jets of high energy plasma produced by directed-explosion weapons like your bazooka: The High Explosive Anti Tank round. This raises fascinating questions of material science. The traditional explanation for how armour works is that materials can be hard but brittle; or soft but tough. Hard armour is resistant to penetration and may shatter projectiles. It is particularly good at stopping fast shells. Tough but soft materials give way before shells, but in elastic deformation --they snap back. They are good against heavy but slower-moving penetrators. Nathan Okun's much-frequented arms and armour pages give a good overview of how this traditional approach to material science. This approach breaks down as we get microscopic. The real explanation of materials resistance to impact turns out to be all quantum mechanical (n and p crystal holes dislocating, electrons moving about). Insofar as we have a model for understanding penetration --or, for that the piston rod hitting the crankshaft-- it is all about thermal energy and conductance.
The reason you don't go ahead and put plastic armour on tanks is probably that it degrades quickly when it is hit. It stops the first round, but is used up in doing it, probably because the shell ends up melting the the hard bits out of the tarry matric. (To explain for those who don't care to follow the link, plastic armour is chunks of road gravel embedded in a solid coal tar matrix. The gravel defeats the penetrant instead of sproinging out of the way because it is held in place by the gluey mass of the tar. the energy of penetration heats the gravel up to a zillion degrees, and the armour melts.)
If you're going to use this scheme, you need to understand how it works, and, in particular, understand the instantaneous physics of energy conductance through these materials. Given that we're dealing with semi-conducting crystallines, I think you can see why I think that there was eventually a crossover to computing science. In the short term, however, understanding the instantaneous consequences of an explosive jet impinging on material has the more militarily important implication of allowing the design of better atom bombs. The Mark 5 atom bomb was the weapon that really made WWIII practicable, and the improvement over WWII's cumbersome makes was entirely in terms of a more efficient arrangement of the explosives that compressed the core. The levitated pit design, first tested in 1948 and independently discovered by the British and Soviets, is often described in homely terms as giving the explosion a rolling start at compressing the core, or some such; but we need to beware of homely analogies because they often mislead us in the realm of the quantum mechanical. I'm not going to try to explain what I think is going on, because I'm frankly working mostly from intuition here, but I am going to suggest that it is science derived from HEAT penetrations of armour.
And that, I think, is where all the thinking about armour and armour penetration has disappeared to between 1945 and 1950, only to come crashing back into the mainstream as a "peasant army" defeats the mighty Americans.
Which, by the way, now that we understand that the Inmun gun was totally unprepared for Seoul to actually fall, and had to take a good long two weeks to reorganise and mobilise for the drive south, could easily not have happened in the first place. As it is, SCAP --and Washington-- had just enough time to organise a response that could be humiliatingly brushed aside in the drive south before securing Pusan and making a fight of it. It's also something of a comedown for us MacArthur haters --pretty much the whole world at this point, I think-- that the American Shogun actually had a pretty good handle on the situation. Perhaps accidentally, but something about generals having to be lucky before they can be smart something.
And speaking of American narcissists, I guess Floating Tom Hutter really has taken his last dive. Now I should probably be realistic and go buy another copy of 2150AD.
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*My copy of Cumming's is a Book Warehouse remaindered copy of the 2005 edition that I probably picked up before 2010, the Book Warehouse having been pretty much gone for at least that long. We're all getting old, and apparently cribbing a book out of Averill Harriman's memoirs gets you a lot more sales than carefully researching the history of Korea for an entire career.
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